This invention relates to an air conditioning system for automotive vehicles, and more particularly to control of a compressor of an air conditioning system of this kind.
Conventional air conditioning systems for automotive vehicles are generally provided with an airflow rate setting switch for setting the flow rate of air discharged from a blower, and a thermostat responsive to temperature of an air outlet of an evaporator for closing or opening to operate or interrupt a compressor. However, the airflow rate setting switch and the thermostat are disposed so as to operate independently of each other. As a result, if the airflow rate setting switch is set to a large airflow rate position in order to obtain a sufficient cooling effect, it is impossible to achieve a desired cooling effect if the setting temperature of the thermostat is relatively high. Also in conventional air conditioning systems for automotive vehicles, which is equipped with a variable delivery compressor, the discharge capacity of the compressor is not always controlled to a sufficiently large value when the airflow rate setting switch is set to a large airflow rate position, thus failing to obtain a desired cooling effect.
Furthermore, if the thermostat is a type having a single setting temperature, the compressor can operate or driven by the engine even when the engine on the vehicle is in a high speed operating condition or in a high load operating condition such as acceleration or running up an ascending slope, where all the engine output should be applied for driving the vehicle. That is, on such an occasion, the engine output becomes insufficient, resulting in degraded driveability.
An air conditioning system for automotive vehicles, equipped with a compressor driven by an engine on the vehicle and disposed to be automatically turned on and off at a setting temperature, or equipped with a variable delivery compressor, has been proposed, e.g. by Japanese Provisional Utility Model Publication No. 57-54411 and Japanese Provisional Utility Model Publication No. 58-28892, which is provided with an economy switch for selectively switching the operation mode of the air conditioning system between normal mode and economy mode, an airflow rate setting switch for setting the airflow rate of the blower, a temperature sensor for detecting temperature at the discharge air outlet of the evaporator, and control means responsive to an output signal from the temperature sensor for effecting on-off control of the compressor in such a manner as to increase the operation rate of the compressor when the economy switch is turned to the normal mode position and to decrease the operation rate of the compressor when the economy switch is turned to the economy mode position.
According to the air conditioning systems of this kind, generally the airflow rate setting switch is turned to a large airflow rate position when the maximum cooling capacity (or maximum heating capacity) is required. However, with the conventional air conditioning system described above, when the economy switch is turned to the economy mode position, the setting temperature of a thermostat, which is an on-off changeover temperature setter, is set to a relatively high value to reduce the operation rate of the compressor. Therefore it is impossible to obtain the maximum cooling capacity so long as the economy switch is held at the normal mode position, even if the airflow rate setting switch is turned to the large airflow rate position.